scholarly journals Continuous measurements of nitrous oxide isotopomers during incubation experiments

2016 ◽  
Author(s):  
Malte Winther ◽  
David Balslev-Harder ◽  
Søren Christensen ◽  
Anders Priemé ◽  
Bo Elberling ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Isotope Effect ◽  
Atmospheric Chemistry ◽  
Isotope Effects ◽  
Denitrifying Bacteria ◽  
Central Position ◽  
Site Preference ◽  
Continuous Measurements ◽  
Incubation Experiments

Abstract. Nitrous oxide (N2O) is an important and strong greenhouse gas in the atmosphere and part of a feed-back loop with climate. N2O is produced by microbes during nitrification and denitrification in terrestrial and aquatic ecosystems. The main sinks for N2O are turnover by denitrification and photolysis and photo-oxidation in the stratosphere. The position of the isotope 15N in the linear N = N = O molecule can be distinguished between the central or terminal position (isotopomers of N2O). It has been demonstrated that nitrifying and denitrifying microbes have a different relative preference for the terminal and central position. Therefore, measurements of the site preference in N2O can be used to determine the source of N2O i.e. nitrification or denitrification. Recent instrument development allows for continuous (on the order of days) position dependent δ15N measurements at N2O concentrations relevant for studies of atmospheric chemistry. We present results from continuous incubation experiments with denitrifying bacteria, Pseudomonas fluorescens (producing and reducing N2O) and P. chlororaphis (only producing N2O). The continuous position dependent measurements reveal the transient pattern (KNO3 to N2O and N2, respectively), which can be compared to previous reported site preference (SP) values. We find bulk isotope effects of −5.5 ‰ ± 0.9 for P. chlororaphis. For P. fluorescens, the bulk isotope effect during production of N2O is −50.4 ‰ ± 9.3 and 8.5 ‰ ± 3.7 during N2O reduction. The values for P. fluorescens are in line with earlier findings, whereas the values for P. chlororaphis are larger than previously published δ15Nbulk measurements from production. The calculations of the SP isotope effect from the measurements of P. chlororaphis result in values of −6.6 ‰ ± 1.8. For P. fluorescens, the calculations results in SP values of −5.7 ‰ ± 5.6 during production of N2O and 2.3 ‰ ± 3.2 during reduction of N2O. In summary, we implemented continuous measurements of N2O isotopomers during incubation of denitrifying bacteria and believe that similar experiments will lead to a better understanding of denitrifying bacteria and N2O turnover in soils and sediments and ultimately hands-on knowledge on the biotic mechanisms behind greenhouse gas exchange of the Globe.

scholarly journals Continuous measurements of nitrous oxide isotopomers during incubation experiments

2017 ◽  
Author(s):  
Malte Winther ◽  
David Balslev-Harder ◽  
Søren Christensen ◽  
Anders Priemé ◽  
Bo Elberling ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Atmospheric Chemistry ◽  
Isotopic Fractionation ◽  
Denitrifying Bacteria ◽  
Site Preference ◽  
Continuous Measurements ◽  
Incubation Experiments ◽  
Soils And Sediments ◽  
Hands On

Abstract. Nitrous oxide (N2O) is an important and strong greenhouse gas in the atmosphere. It is produced by microbes during nitrification and denitrification in terrestrial and aquatic ecosystems. The main sinks for N2O are turnover by denitrification and photolysis and photo-oxidation in the stratosphere. In the linear N = N = O molecule 15N substitution is possible in two distinct positions, central and terminal. The respective molecules, 14N15N16O and 15N14N16O, are called isotopomers. It has been demonstrated that N2O produced by nitrifying or denitrifying microbes exhibits a different relative abundance of the isotopomers. Therefore, measurements of the site preference (difference in the abundance of the two isotopomers) in N2O can be used to determine the source of N2O i.e. nitrification or denitrification. Recent instrument development allows for continuous position dependent δ15N measurements at N2O concentrations relevant for studies of atmospheric chemistry. We present results from continuous incubation experiments with denitrifying bacteria, Pseudomonas fluorescens (producing and reducing N2O) and Pseudomonas chlororaphis (only producing N2O). The continuous analysis of N2O isotopomers reveal the transient pattern (KNO3 to N2O and N2, respectively). We find bulk isotopic fractionation of −5.01 ‰ ± 1.20 for P. chlororaphis, in line with previous results for production from denitrification. For P. fluorescens, the bulk isotopic fractionation during production of N2O is −52.21 ‰ ± 9.28 and 8.77 ‰ ± 4.49 during N2O reduction. The SP isotopic fractionation for P. chlororaphis is −3.42 ‰ ± 1.69. For P. fluorescens, the calculations result in SP isotopic fractionation values of 5.73 ‰ ± 5.26 during production of N2O and 2.41 ‰ ± 3.04 during reduction of N2O. We interpret the slightly increased isotopic fractionation during reduction to diffusive isotopic fractionation and a difference in active enzymes during production of N2O. In summary, we implemented continuous measurements of N2O isotopomers during incubation of denitrifying bacteria and believe that similar experiments will lead to a better understanding of denitrifying bacteria and N2O turnover in soils and sediments and ultimately hands-on knowledge on the biotic mechanisms behind greenhouse gas exchange of the globe.

scholarly journals Continuous measurements of nitrous oxide isotopomers during incubation experiments

2018 ◽  
Vol 15 (3) ◽  
pp. 767-780 ◽  
Author(s):  
Malte Winther ◽  
David Balslev-Harder ◽  
Søren Christensen ◽  
Anders Priemé ◽  
Bo Elberling ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Atmospheric Chemistry ◽  
Isotopic Fractionation ◽  
Denitrifying Bacteria ◽  
Site Preference ◽  
Continuous Measurements ◽  
Incubation Experiments ◽  
Soils And Sediments ◽  
Hands On

Abstract. Nitrous oxide (N2O) is an important and strong greenhouse gas in the atmosphere. It is produced by microbes during nitrification and denitrification in terrestrial and aquatic ecosystems. The main sinks for N2O are turnover by denitrification and photolysis and photo-oxidation in the stratosphere. In the linear N = N = O molecule 15N substitution is possible in two distinct positions: central and terminal. The respective molecules, 14N15N16O and 15N14N16O, are called isotopomers. It has been demonstrated that N2O produced by nitrifying or denitrifying microbes exhibits a different relative abundance of the isotopomers. Therefore, measurements of the site preference (difference in the abundance of the two isotopomers) in N2O can be used to determine the source of N2O, i.e., nitrification or denitrification. Recent instrument development allows for continuous position-dependent δ15N measurements at N2O concentrations relevant for studies of atmospheric chemistry. We present results from continuous incubation experiments with denitrifying bacteria, Pseudomonas fluorescens (producing and reducing N2O) and Pseudomonas chlororaphis (only producing N2O). The continuous measurements of N2O isotopomers reveals the transient isotope exchange among KNO3, N2O, and N2. We find bulk isotopic fractionation of −5.01 ‰ ± 1.20 for P. chlororaphis, in line with previous results for production from denitrification. For P. fluorescens, the bulk isotopic fractionation during production of N2O is −52.21 ‰ ± 9.28 and 8.77 ‰ ± 4.49 during N2O reduction.The site preference (SP) isotopic fractionation for P. chlororaphis is −3.42 ‰ ± 1.69. For P. fluorescens, the calculations result in SP isotopic fractionation values of 5.73 ‰ ± 5.26 during production of N2O and 2.41 ‰ ± 3.04 during reduction of N2O. In summary, we implemented continuous measurements of N2O isotopomers during incubation of denitrifying bacteria and believe that similar experiments will lead to a better understanding of denitrifying bacteria and N2O turnover in soils and sediments and ultimately hands-on knowledge on the biotic mechanisms behind greenhouse gas exchange of the globe.

scholarly journals Oxygen isotope fractionation during N<sub>2</sub>O production by soil denitrification

2016 ◽  
Vol 13 (4) ◽  
pp. 1129-1144 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jens Dyckmans ◽  
Jan Kaiser ◽  
Alina Marca ◽  
Jürgen Augustin ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Effect ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
N2o Production ◽  
Oxygen Isotope Fractionation ◽  
Oxygen Isotope Exchange ◽  
Incubation Experiments

Abstract. The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O ∕ 16O ratio of soil water and the N2O product of δ18O(N2O ∕ H2O)  =  (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O ∕ H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O ∕ H2O) showed a significant correlation (R2 = 0.70, p <  0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification, isotope exchange occurs prior to isotope branching and that this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰, in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects.

scholarly journals Is site preference of N2O a tool to identify benthic denitrifier N2O?

2013 ◽  
Vol 10 (4) ◽  
pp. 281 ◽  
Author(s):  
Aurélie Mothet ◽  
Mathieu Sebilo ◽  
Anniet M. Laverman ◽  
Véronique Vaury ◽  
André Mariotti
Keyword(s):  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Nitrate Reduction ◽  
Reduction Rate ◽  
Aquatic Environments ◽  
Site Preference ◽  
Reduction Step ◽  
Oxide Reduction ◽  
Nitrous Oxide Reduction ◽  
Highly Correlated

Environmental context The greenhouse gas nitrous oxide is produced by bacteria and emitted from terrestrial and aquatic environments; the origin of this compound can be determined by its 15N intramolecular distribution (site preference). The site preference of nitrous oxide was characterised experimentally in bacterial denitrifying communities under controlled conditions. This study shows the importance of the last step of denitrification on the site preference values, and that complementary methods are necessary to identify the sources of nitrous oxide. Abstract Site preference values of nitrous oxide emitted during different steps of benthic denitrification were determined. Compared to that of nitrous oxide as end product, the site preference during complete denitrification presents a large variation, due to the final step, and is highly correlated with nitrate reduction rate. The nitrous oxide reduction step appears decisive on the site preference values.

scholarly journals Estimation of isotope variation of N<sub>2</sub>O during denitrification by <i>Pseudomonas aureofaciens</i> and <i>Pseudomonas chlororaphis</i>: implications for N<sub>2</sub>O source apportionment

2018 ◽  
Vol 15 (12) ◽  
pp. 3873-3882 ◽  
Author(s):  
Joshua A. Haslun ◽  
Nathaniel E. Ostrom ◽  
Eric L. Hegg ◽  
Peggy H. Ostrom
Keyword(s):  
Nitrous Oxide ◽  
Electron Donor ◽  
Isotope Effects ◽  
Microbial Processes ◽  
Site Preference ◽  
N2o Emissions ◽  
Pseudomonas Chlororaphis ◽  
Fractionation Factor ◽  
N2o Production ◽  
Soil Microbial

Abstract. Soil microbial processes, stimulated by agricultural fertilization, account for 90 % of anthropogenic nitrous oxide (N2O), the leading source of ozone depletion and a potent greenhouse gas. Efforts to reduce N2O flux commonly focus on reducing fertilization rates. Management of microbial processes responsible for N2O production may also be used to reduce N2O emissions, but this requires knowledge of the prevailing process. To this end, stable isotopes of N2O have been applied to differentiate N2O produced by nitrification and denitrification. To better understand the factors contributing to isotopic variation during denitrification, we characterized the δ15N, δ18O and site preference (SP; the intramolecular distribution of 15N in N2O) of N2O produced during NO3- reduction by Pseudomonas chlororaphis subsp. aureofaciens and P. c. subsp. chlororaphis. The terminal product of denitrification for these two species is N2O because they lack the gene nitrous oxide reductase, which is responsible for the reduction of N2O to N2. In addition to species, treatments included electron donor (citrate and succinate) and electron donor concentration (0.01, 0.1, 1 and 10 mM) as factors. In contrast to the expectation of a Rayleigh model, all treatments exhibited curvilinear behaviour between δ15N or δ18O and the extent of the reaction. The curvilinear behaviour indicates that the fractionation factor changed over the course of the reaction, something that is not unexpected for a multi-step process such as denitrification. Using the derivative of the equation, we estimated that the net isotope effects (η) vary by as much as 100 ‰ over the course of a single reaction, presenting challenges for using δ15N and δ18O as apportionment tools. In contrast, SP for denitrification was not affected by the extent of the reaction, the electron donor source or concentration, although the mean SP of N2O produced by each species differed. Therefore, SP remains a robust indicator of the origin of N2O. To improve apportionment estimates with SP, future studies could evaluate other factors that contribute to the variation in SP.

scholarly journals Supplementary material to "Continuous measurements of nitrous oxide isotopomers during incubation experiments"

2016 ◽  
Author(s):  
Malte Winther ◽  
David Balslev-Harder ◽  
Søren Christensen ◽  
Anders Priemé ◽  
Bo Elberling ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Continuous Measurements ◽  
Incubation Experiments ◽  
Supplementary Material

scholarly journals Supplementary material to "Continuous measurements of nitrous oxide isotopomers during incubation experiments"

2017 ◽  
Author(s):  
Malte Winther ◽  
David Balslev-Harder ◽  
Søren Christensen ◽  
Anders Priemé ◽  
Bo Elberling ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Continuous Measurements ◽  
Incubation Experiments ◽  
Supplementary Material

scholarly journals Oceanic phytoplankton are a potentially important source of benzenoids to the remote marine atmosphere

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Manon Rocco ◽  
Erin Dunne ◽  
Maija Peltola ◽  
Neill Barr ◽  
Jonathan Williams ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Dimethyl Sulfide ◽  
Laboratory Culture ◽  
Marine Phytoplankton ◽  
Marine Atmosphere ◽  
Aerosol Formation ◽  
Incubation Experiments ◽  
Phytoplankton Communities ◽  
Anthropogenic Air Pollutants ◽  
Benzene Toluene

AbstractBenzene, toluene, ethylbenzene and xylenes can contribute to hydroxyl reactivity and secondary aerosol formation in the atmosphere. These aromatic hydrocarbons are typically classified as anthropogenic air pollutants, but there is growing evidence of biogenic sources, such as emissions from plants and phytoplankton. Here we use a series of shipborne measurements of the remote marine atmosphere, seawater mesocosm incubation experiments and phytoplankton laboratory cultures to investigate potential marine biogenic sources of these compounds in the oceanic atmosphere. Laboratory culture experiments confirmed marine phytoplankton are a source of benzene, toluene, ethylbenzene, xylenes and in mesocosm experiments their sea-air fluxes varied between seawater samples containing differing phytoplankton communities. These fluxes were of a similar magnitude or greater than the fluxes of dimethyl sulfide, which is considered to be the key reactive organic species in the marine atmosphere. Benzene, toluene, ethylbenzene, xylenes fluxes were observed to increase under elevated headspace ozone concentration in the mesocosm incubation experiments, indicating that phytoplankton produce these compounds in response to oxidative stress. Our findings suggest that biogenic sources of these gases may be sufficiently strong to influence atmospheric chemistry in some remote ocean regions.

scholarly journals Greenhouse gas emissions from the water–air interface of a grassland river: a case study of the Xilin River

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Xue Hao ◽  
Yu Ruihong ◽  
Zhang Zhuangzhuang ◽  
Qi Zhen ◽  
Lu Xixi ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Land Use ◽  
Nitrous Oxide ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Ghg Emissions ◽  
Nitrous Oxide Emissions ◽  
Gas Emissions ◽  
Sand Land ◽  
Very High

AbstractGreenhouse gas (GHG) emissions from rivers and lakes have been shown to significantly contribute to global carbon and nitrogen cycling. In spatiotemporal-variable and human-impacted rivers in the grassland region, simultaneous carbon dioxide, methane and nitrous oxide emissions and their relationships under the different land use types are poorly documented. This research estimated greenhouse gas (CO2, CH4, N2O) emissions in the Xilin River of Inner Mongolia of China using direct measurements from 18 field campaigns under seven land use type (such as swamp, sand land, grassland, pond, reservoir, lake, waste water) conducted in 2018. The results showed that CO2 emissions were higher in June and August, mainly affected by pH and DO. Emissions of CH4 and N2O were higher in October, which were influenced by TN and TP. According to global warming potential, CO2 emissions accounted for 63.35% of the three GHG emissions, and CH4 and N2O emissions accounted for 35.98% and 0.66% in the Xilin river, respectively. Under the influence of different degrees of human-impact, the amount of CO2 emissions in the sand land type was very high, however, CH4 emissions and N2O emissions were very high in the artificial pond and the wastewater, respectively. For natural river, the greenhouse gas emissions from the reservoir and sand land were both low. The Xilin river was observed to be a source of carbon dioxide and methane, and the lake was a sink for nitrous oxide.

scholarly journals Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Paul M. Magyar ◽  
Damian Hausherr ◽  
Robert Niederdorfer ◽  
Nicolas Stöcklin ◽  
Jing Wei ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Anammox Bacteria ◽  
Ammonium Oxidation ◽  
Experimental Conditions ◽  
N Transformations ◽  
Natural Systems ◽  
Inverse Isotope Effect

AbstractAnaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (15N/14N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor 15ε for the reduction of nitrite to N2 is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of 15ε for the oxidation of nitrite to nitrate (inverse isotope effect, − 16 to − 43‰) and for the reduction of ammonium to N2 (normal isotope effect, 19–32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.

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